Trailbraking Works: Pocono North Corvette Data Analysis

Published: May 20, 2015

At a recent Riesentoter PCA event I had an opportunity to validate one particular theory - that trailbraking into a corner is faster, in terms of lap time, than not, even for high power cars. In low and medium power cars trailbraking is pretty much a staple of my driving style. Does trailbraking still apply to high power cars running late apexes? It turns out that it does!

At this event I went out for a session as a passenger in a C5 Corvette Z06 with the car's owner driving. The car was on Toyo R888 tires which felt pretty good but had 40-50 heat cycles on them. The car did well in braking zones and the driver executed late apexes well, but the impression I got was that there was a bunch of grip left unused at corner entry - in other words, the entry speed in most corners was lower than what the car would have been capable of with trailbraking.

I drove the car in the following session on Nitto NT01 tires. NT01 offer a similar level of grip to R888, making the lap time comparison somewhat valid. I felt that NT01 offered less grip than the R888 that came off the car, despite the fact that R888 had many more heat cycles than NT01.

Below are speed traces for the car owner driving (black), me driving (green) and a C6 Z06 Corvette on Hoosiers that I was in earlier the same day (red). The C6Z trace is there to provide a reference for how fast the same car on grippier tires might take corners.

The most obvious difference between the cars is in turn 1, although it does not have much to do with trailbraking. This is a difference largely of driving style and confidence - many drivers brake for turn 1 and accelerate between turns 1 and 2 whereas my goal is to carry the most speed from the trioval through the transition in turn 1 and brake primarily appoaching turn 2. As I had limited seat time in a Corvette on Pocono North (just this one session, in fact) I did not take turn 1 very aggressively. The car in its configuration probably could take turn 1 at 105-115 mph with some more seat time. Even so I was much quicker through turn 1 than both the car owner and the C6Z reference on Hoosiers, whose driver used the brake-for-turn-1 approach.

Beside turn 1 though the difference between black and green lines is textbook trailbraking. I achieve similar speeds on the straights compared to the car owner, brake at the same rate, but then trailbrake into corners which produces rounded U speed traces in the valleys compared to angular Vs. Once trailbraking is complete and I start to accelerate, the car is traveling as quickly as it was with the owner driving it with late apex lines. As such I do not get an exit speed advantage - all of the time I make up happens in corner entry and mid corner. I gain time mid corner because trailbraking typically yields a higher minimum corner, or apex, speed - as there is more weight on the front tires the car turns better, hence is able to traverse the hard cornering portion of each turn faster.

I do give up some time on the main straight due to shifting earlier.

There was one weird aspect of trailbraking on this particular C5Z. On the first couple of laps as I eased off the brake pedal and started to add steering angle the car, instead of rotating into the turn, locked up a front tire and continued in a straight line. There is no ABS in this car which is unusual for a Corvette. The forward to lateral traction split seems to be different in a Corvette compared to low power cars I am used to. It is also possible that the car simply wants more tire, and tallying up my experiences with NT01 tires I think NT01 do offer less grip than Toyo R888.

Would trailbraking be applicable if the car had more grip? I would say yes. Looking at an earlier analysis of another C5 Z06 Corvette at Lightning, even though most gains made by the faster driver came from running later apexes and as a result going to full throttle earlier, trailbraking is plainly visible in turns 1 and 9 and it is beneficial in both corners.

Tagged: data analysis